Cellular and molecular biologists in the Dept. of Biological Sciences at the Univ. of Southern California have a pressing need for a modern, high-throughput transmission electron microscope. Existing instruments (more than 17 years old) are inadequate because of obsolete vacuum tube electronics requiring extensive maintenance (when parts are available), manual valve operation, and severely restricted film capacity. They are housed in facilities that are heavily used for instruction and are furnished with out-of-date equipment that cannot tolerate high volume use. It is proposed to acquire a JEOL 100XC or equivalent instrument to be housed in a university-renovated laboratory in the Ahmanson Center for Biological Research. Major factors in instrument selection are ease of routine operation, ease of specimen change (for analysis serial sections or heteroduplexes of DNA or RNA), and efficient photography (for photomontages and histograms). In addition, high resolution and contrast at high magnification are required for examining electron-opaque reaction products in enzyme cytochemistry studies, and accelerating voltages of 80 kV or higher are needed for studying freeze-fracture replicas. Publication records and funding levels indicate that the applicants are performing good research in significant areas of modern biology. The molecular biology projects include studies of specialized recombination by heteroduplex analysis, studies of regulation of gene expression during embryogenesis, and investigations of replicative intermediates during Epstein-Barr virus infection and transformation. All three of these projects involve cloning, which requires electron microscope analysis of recombinant molecules. Other applicants are using enzyme cytochemistry in liver plasma membranes to elucidate the insulin activation of cyclic AMP tissue resulting from exposure to atmospheric pollutants. The cellular biologists are studying the ultrastracture of synapses and sensory organs in lower vertebrates. These include freeze-fracture studies on formation of neuromuscular junctions, studies on structural correlates of changes in synaptic effectiveness, and mechanisms of transmitter release and regulation.